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Debt (5.875% Senior Notes) (Details) - Senior Notes - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Oct. 03, 2013
Mar. 19, 2013
5.875% Senior Notes due 2022        
Debt Instrument [Line Items]        
Stated interest rate 5.875% 5.875%    
Debt instrument, face amount     $ 250,000,000.0  
Debt instrument, coupon rate 5.875%      
Debt instrument, yield to maturity 5.875%      
Debt instrument, payment terms Interest on the 5.875% Senior Notes due 2022 is payable semi-annually in cash in arrears on January 15 and July 15, commencing on January 15, 2014.      
Debt instrument, frequency of payment semi-annually      
Debt instrument, commencement date of first required payment Jan. 15, 2014      
Debt instrument, maturity date Jan. 15, 2022      
Percentage of principal amount redeemable 101.00%      
5.875% Senior Notes due 2022 | Minimum | Redemption, Period on or Prior To April 1, 2018        
Debt Instrument [Line Items]        
Notice period prior to redemption 30 days      
5.875% Senior Notes due 2022 | Maximum | Redemption, Period on or Prior To April 1, 2018        
Debt Instrument [Line Items]        
Notice period prior to redemption 60 days      
5.125% Senior Notes due 2023        
Debt Instrument [Line Items]        
Stated interest rate 5.125% 5.125%   5.125%
Debt instrument, face amount       $ 300,000,000.0
Debt instrument, coupon rate 5.125%      
Debt instrument, yield to maturity 5.125%      
Debt instrument, payment terms Interest is payable semi-annually on April 1 and October 1 each year, beginning October 1, 2013.      
Debt instrument, frequency of payment semi-annually      
Debt instrument, commencement date of first required payment Oct. 01, 2013      
Debt instrument, maturity date Apr. 01, 2023      
Percentage of principal amount redeemable 101.00%      
Violation or event of default, interest payment failure, term 30 days      
Violation or event of default, interest payment failure, maximum excess proceeds on sale of asset $ 25,000,000.0      
Violation or event of default, interest payment failure, failure to comply with other indenture agreements, term 60 days      
5.125% Senior Notes due 2023 | Minimum | Redemption, Period on or Prior To April 1, 2018        
Debt Instrument [Line Items]        
Notice period prior to redemption 30 days      
5.125% Senior Notes due 2023 | Maximum | Redemption, Period on or Prior To April 1, 2018        
Debt Instrument [Line Items]        
Notice period prior to redemption 60 days